Mobile electronic devices incorporating a touch screen have become increasingly popular in recent years. A touch screen offers a fast and flexible control of a mobile electronic device. Conventional touch screens use e.g. a resistive touch panel to detect a single touch, whereas more advanced touch screens may use a capacitive touch screen panel capable of detecting multiple simultaneous touches. This so-called multi-touch technology can also be realized using an optical touch screen, wherein optical sensors are integrated in e.g. an LCD display matrix.
When a mobile electronic device is transported by a user, it is often brought into a locked state, or sleep mode, wherein the touch screen of the mobile electronic device is deactivated. In the locked state, an accidental activation of control elements is prevented, and power consumption is reduced. Locking and unlocking of such a mobile electronic device generally occurs by using dedicated mechanical buttons. For example for unlocking the device, a first button has to be pressed, upon which a screen is activated with instructions for pressing a second button. After pressing the second button, the mobile electronic device is finally unlocked.
In such a conventional mobile electronic device, the screen is activated even if the first button is only accidentally pressed, e.g. when carrying the device in a pocket. This leads to an undesirable increase in power consumption. Further, mechanical buttons need to be provided. These require additional space on a face plate of the mobile electronic device. Even though two buttons may need to be pressed, this may also accidentally occur when carrying the device in a pocket, resulting in operation of the device in an unlocked mode. Accordingly, the device may unintentionally be operated, which may lead to an unwanted placement of calls and associated costs, as well as a reduced battery life. It is thus desirable to provide a more controlled unlocking of the mobile electronic device. The unlocking mechanism should also be user-friendly, i.e. provide a straight forward and ergonomic unlocking of the device. It is also desirable to reduce the amount of space required by mechanical control elements, so that a large display can be realized.